Articulations
8.1 Functions of Joints
Functions of Joints (Articulations)—Connect two bones
Joints Enable Movement—Surrounding muscles and tendons exert the necessary amount of force across the joint allowing movement
Joints Provide Stability—Joints that allow limited or no mobility are very stable; Critical for joints that protect underlying structures, such as those in the skull
Joints Allow Long Bones to Lengthen—The Epiphyseal Plate, a temporary joint, is the location in long bones that grow in length during skeletal development
Functional Classification—Based on the amount of movement, and the degree of stability
Synarthrosis—No movement between articulating bones; Provides most stability
Amphiarthrosis—Small amount of movement between articulating bones; Provides a significant amount of stability
Diarthrosis—Freely moveable with a wide variety of specific movements; Provides the least amount of stability
Structural Classification—Based on the type of connective tissue that links the bones, and the presence or absence of a space between the bones
Fibrous Joints—United by dense regular collagenous connective tissue; No joint space; Functionally synarthroses or amphiarthroses
Cartilaginous Joints—Cartilage between the articulating bones; No joint space; Functionally synarthroses or amphiarthroses
Synovial Joints—Have a joint cavity, filled with fluid between articulating bones; Functionally diarthroses
Fibrous Joints—Collagen fibers found in these joints lend stability but permit little, if any, motion
Sutures—Joint between bones of the skull; Edges of skull bones have finger-like projections that interweave and are held together by very short collagen fibers; Very stable synarthroses; During the fourth or fifth decade of life, the bones may begin to fuse forming a Synostosis
Gomphoses—Joint between a tooth and its corresponding alveolus in the mandible or maxilla; Each tooth is firmly attached to the bone fibers collectively called the Periodontal Ligament; Stable synarthroses
Syndesmoses—Articulating bones are joined by an Interosseous Membrane or Ligament; Composed of dense regular collagenous connective tissue
Found between the radius and ulna in the forearm and between the fibula and tibia in the leg; Amphiarthroses because allow limited movement
Cartilaginous Joints—Lack a joint cavity and allow for little, if any, motion
Synchondroses—Bones united by Hyaline Cartilage; Synarthroses
Includes the epiphyseal plate found between the diaphysis and epiphysis of a growing long bone; When the cartilage in the plate is replaced by bone, a synostosis is formed
Includes the first sternocostal joint, where the first rib attaches to the manubrium, and the costochondral
Cartilaginous Joints (continued)
Symphyses—Bones united by a Fibrocartilage Pad; Amphiarthroses
Includes the intervertebral joints or intervertebral discs, between successive vertebral bodies; Each intervertebral joint allows a small degree of motion, but the spinal column as a whole is quite flexible
Includes the pubic symphysis between the two pubic bones of the pelvic girdle; Flexible during childbirth in women to create a larger opening for the head of the newborn
Epiphyseal plate in a child’s long bone is one of the weakest parts of a developing skeleton
Fractures may result in lifelong consequences, such as differences in limb length, limb deformities, and early-onset arthritis if not managed properly
Recreational activities, accidents, and competitive athletics are common causes with the plates of the long bones of the forearms being the most commonly affected
Swelling, pain, and redness are symptoms
Minor fractures generally require immobilizing the joint with a cast, while severe fractures usually require surgery
Joint (Synovial) Cavity—Space between two 2 articulating bones
Articular Capsule—Double-layered structure; Outer Fibrous Layer is dense irregular connective tissue that holds bones together and keeps out blood supply; Inner Synovial Membrane layer is loose connective tissue with cells that secrete Synovial Fluid, which has three functions:
Lubrication—Reduces friction and protects the articulating ends of the bones
Metabolic Functions—Supplies nutrients, such as glucose, to the cells in the joint cavity; Removes metabolic wastes
Shock Absorption—Evenly distributes the force and stress on the articular surfaces of the bones during movement
Synovial fluid is continuously replenished, circulated, and removed; Too little fluid can result in joint damage; Too much can cause pain and impair joint mobility
Joint (Synovial) Cavity—Space between two 2 articulating bones
Articular Capsule—Double-layered structure; Outer Fibrous Layer is dense irregular connective tissue that holds bones together and keeps out blood supply; Inner Synovial Membrane layer is loose connective tissue with cells that secrete Synovial Fluid, which has three functions:
Lubrication—Reduces friction and protects the articulating ends of the bones
Metabolic Functions—Supplies nutrients, such as glucose, to the cells in the joint cavity; Removes metabolic wastes
Shock Absorption—Evenly distributes the force and stress on the articular surfaces of the bones during movement
Synovial fluid is continuously replenished, circulated, and removed; Too little fluid can result in joint damage; Too much can cause pain and impair joint mobility
Joint (Synovial) Cavity (continued)
Articular Cartilage—Hyaline cartilage covers all exposed articulating bone surfaces within a joint cavity; Smooth surface that reduces friction and absorbs shock; Avascular so depends on circulation of synovial fluid; Injuries may result in permanent damage due to the lack of direct blood supply
Other Components—Adipose Tissue provides protective padding; Blood Vessels, which surround the articular capsule; Nerves transmit painful stimuli to the brain and stimuli relating to position of the joint to help with body movement and postural adjustments
Ligaments—Dense regular collagenous connective tissue structure that connects one bone to another bone
Intrinsic Ligaments—Thickened regions of the articular capsule; Found within the capsule
Extrinsic Ligaments—Not part of the articular capsule that may be inside or outside the joint cavity
Tendons—Dense regular collagenous connective tissue structure that connects a muscle to a bone or other structure; Pull on bones during muscle contractions; Stabilize joints that they cross over; Muscles keep the tendons taut with small contractions called Muscle Tone
Bursae—Synovial fluid-filled structure lined with a synovial membrane; Found in regions of high stress where bones, tendons, muscles, and skin interact in a small space to minimize friction
Tendon Sheaths—Long bursae that surround some tendons in high-stress regions of the body; Protect long tendons as they course over and around synovial joints
Bursaitis—Inflammation of a bursa, most commonly in the shoulder, elbow, hip, and knee
Can result from a single traumatic event, such as a fall, repetitive movements, such as throwing a ball, or inflammatory disease, such as arthritis
Symptoms include pain at rest and with movement of the joint, tenderness, swelling, and warmth
Rest, ice, compression of the injured area, and anti-inflammatory medications are beneficial in the early stages of the injury; Anti-inflammatory steroid injections into the bursa, and fluid removed from the bursa may also be used
Arthritis—Inflammation of one or more joints, resulting in pain, joint stiffness, and decreased range of motion; Results from breakdown of articular cartilage
Osteoarthritis—Most common form; Occurs from wear and tear, injuries, and advanced age
Rheumatoid Arthritis—Autoimmune disease that results in joint destruction mediated by the individual’s own immune system
Gouty Arthritis (Gout) —Joint damage due to inflammatory reaction to excess Uric Acid Crystal deposits
Bones in a synovial joint travel through a plan around an imaginary line called an Axis; Each plane has an axis that is perpendicular to its flat surface; Joints are grouped into classes based on the number of axes around which a bone can move
Nonaxial Joints—Motion occurs in one or more planes, but do not move around an axis
Uniaxial Joints—Motion around one axis
Biaxial Joints—Motion around two axes
Multiaxial (Triaxial) Joints—Motion around three axes
The elbow joint has only 1 one axis that acts like a hinge
Allows motion in one 1 plane perpendicular to the axis
Allows the forearm and hand to move toward the shoulder or to move in the opposite direction
The metacarpophalangeal joints can move around axis one, allowing phalanges to move toward or away from the palm
These joints can also move around axis two, allowing the fingers to squeeze together or fan apart
The shoulder joint moves forward and backward (axis one); away from and toward the body (axis two); rotate, or move in a circular pattern (axis three)
Gliding Movements—Sliding motion between the articulating surfaces of the bones in a joint
Nonaxial because bones slide past each other in a single plane not around an axis
Direction depends on the shape of the bones and the supporting structures
Gliding movements of synovial joints.
Angular Movements—Increase or decrease the angle between the articulating bones
Flexion and Extension
Flexion—Decreases the angle between articulating bones by bringing the two bones closer together; Lateral flexion is sideways movement
Extension—Increases the angle between articulating bones
Hyperextension—Extension beyond the anatomical position of the joint
Angular movements: flexion and extension of synovial joints.
Angular Movements (continued)
Abduction and Adduction
Abduction—Motion of a body part away from the midline of the body or another reference point (such as the midline of the hand or foot)
Adduction—Motion of a body part toward the midline of the body or some other reference point
Circumduction—A freely moveable distal bone moves around a stationary proximal bone in a cone-shaped motion; Sum total of flexion-extension and abduction-adduction movements; Best seen at the hip and shoulder joints
Angular Movements (continued)
Rotation—Nonangular, pivoting motion; One bone rotates or twists on the Longitudinal Axis running down the middle
Internal (Medial) Rotation—Rotates body part toward the midline
External (Lateral) Rotation—Rotates body part away from the midline
Angular Movements (continued)
Rotation—The bone turns around itself
Circumduction—The bone can move in a circle around something else
Special Movements—Movements not well described by the previous categories or that pertain to only one or a few joints
Opposition and Reposition
Opposition—Occurs at the thumb; Involves movement of the thumb across the palmar surface of the hand
Reposition—Return of the thumb to anatomical position
Depression and Elevation
Depression—Movement of a body part in an inferior direction
Elevation—Opposite of depression
Figure 8.9 Special movements of synovial joints a, b, c and d
Special Movements (continued)
Protraction and Retraction
Protraction—Moves a body part in the anterior direction
Retraction—Moves a body part posteriorly
Inversion and Eversion
Inversion—Rotational movement of the foot in which the plantar surface rotates medially toward the midline
Eversion—The plantar surface of the foot rotates laterally away from the midline
Figure 8.9 Special movements of synovial joints e, f, g and h
Special Movements (continued)
Dorsiflexion and Plantarflexion
Dorsiflexion—The angle between the foot and the tibia decreases; Toes are pulled towards the head
Plantarflexion—The angle between the foot and the tibia increases; Toes point toward the ground
Supination and Pronation
Supination—Forearm is supinated when palm faces anteriorly with the thumb pointing laterally
Pronation—Turn the palmar surface medially until it faces posteriorly with the thumb pointing medially
Range of Motion—The amount of movement a joint is capable of under normal circumstances
Nonaxial Joints, such as the intercarpal joints, tend to have the smallest range of motion
Multiaxial Joints, such as the shoulder, tend to have the greatest range of motion
Study Boost: Keeping Synovial Joint Movements Straight with Memory Clues
Abduction—You abduct it or take it away
Adduction—You add the part back to the body
Plantarflexion—You plant your foot on the ground
Inversion—You turn your foot inward
Supination—You hold soup when your hand is supinated
Pronation—You pour it out when your hand is pronated
You make a fist when you oppose someone (opposition)
If someone is depressed, they are slumped down, requiring the motion of depression
Structural Classes of Synovial Joints—The amount of motion a joint allows is determined by the shape of the surfaces of the two articulating bones and the number of axes around which the bones move
Plane Joint—Nonaxial joint; Two bones whose flat surfaces sit next to each other
Hinge Joint—Uniaxial joint; Convex surface of one bone fits into a concave depression of another bone
Pivot Joint—Uniaxial joint; The rounded surface of one bone fits into a groove on the surface of another bone; A ring-like ligament surrounds the rounded bone and holds it in the groove of the other bone
Condylar (Ellipsoid) Joint—Biaxial joint; The oval, convex surface of one bone fits into a shallow concave surface of another bone
Structural Classes of Synovial Joints (continued)
Saddle Joint—Biaxial joint; Surface of each articulating bone has both convex and concave regions that complement each other
Ball-and-Socket Joint—Multiaxial joint; Articulating surface of one bone is ball-shaped, or spherical, and fits into a cup or socket formed by the articulating surface of the other bone
The six types of synovial joints and the motion allowed at each.
Fibrous and Cartilaginous Joints
Synovial Joints
The Elbow —Hinge joint composed of two articulations
Humeroulnar Joint—Between the trochlea of the humerus and the trochlear notch of the ulna
Humeroradial Joint—Between the capitulum of the humerus and the head of the radius
Extrinsic ligaments support the articular capsule:
Radial (Lateral) Collateral Ligament—Supports the lateral side of the joint
Ulnar (Medial) Collateral Ligament—Supports the medial side of the joint
Anular Ligament—Stabilizes the radial head
Anatomical structure of the elbow joint.
The Knee—Largest diarthrosis in the body; Hinge joint that also allows some degree of rotation and lateral gliding; Can “lock out” in extension without causing muscle fatigue; Composed of two articulations
Tibiofemoral Joint—Between the femoral and tibial condyles
Patellofemoral Joint—Between the patella and the patellar surface of the femur
Articular capsule covers all but the anterior surface of the knee joint, which is covered by the patella, the tendon of the quadriceps femoris muscle group, and the patellar ligament
The Knee (continued)
Menisci and extrinsic ligaments that enhance stability:
Medial and Lateral Menisci—Pair of C-shaped fibrocartilage pads on the tibial condyles; Improve fit between bones; Shock absorption and cushioning
Tibial (Medial) Collateral Ligament—Links femur with the tibia and attaches to the medial meniscus
Fibular (Lateral) Collateral Ligament—Links femur with the fibula but does not attach to the lateral meniscus
The Knee (continued)
Anterior Cruciate Ligament (A C L) —Runs from an anterior insertion site on the tibia to the posterior aspect of the femur; Prevents tibia from moving too far anteriorly
Posterior Cruciate Ligament (P C L) —Runs from a posterior position on the tibia to the anterior femur; Prevents tibia from moving too far posteriorly
Any activity that involves quick changes in direction can injure the knee
Contact sports, such as football or soccer, put athletes at greater risk, especially if their knee is struck from the side or from behind
Lateral blows often rupture the tibial collateral ligament, and puts pressure on the lateral meniscus, which may tear; The force of the blow also frequently ruptures the anterior cruciate ligament, forming the so-called Unhappy Triad
Surgery is required to repair the injury followed by physical therap
The Shoulder (Glenohumeral Joint) —Made up of the ball-shaped humeral head and the glenoid cavity on the lateral scapula; Multiaxial ball-and-socket joint; Most freely moveable joint in the body, which makes it unstable
Articular capsule is reinforced by several structures:
Tendon of the long head of the biceps brachii muscle
Coracohumeral Ligament
Three Glenohumeral Ligaments (may or may not be present)
Two prominent bursae to reduce friction: Subacromial Bursa and the Subscapular Bursa
The Shoulder (Glenohumeral Joint) (continued)
Tendons of the four other muscles (the Rotator Cuff):
Subscapularis (anteriorly)
Supraspinatus, Infraspinatus, Teres Minor (posteriorly)
Glenoid Labrum—Fibrocartilaginous ring that sits on the rim of the glenoid cavity
Dislocated Shoulder—Involves glenohumeral joint with traumatic displacement of the head of the humerus from the glenoid cavity
Separated Shoulder—Involves acromioclavicular joint, which is not a component of the shoulder
Most (90%) of dislocations occur through the inferior part of the anterior capsule, which is the weakest part
Falls and contact sports are common causes of dislocations
Minor dislocations can “pop” back into place, but more severe injuries may require surgical repair
The Hip (Coxal Joint) —Articulation between the acetabulum and the ball-shaped head of the femur; Multiaxial ball-and-socket joint; More stable than the shoulder joint
Acetabular Labrum—Fibrocartilage ring strengthens the fit between the bones
Supported by a strong articular capsule
Supported by many large, powerful muscle groups that surround it
The Hip (Coxal Joint) (continued)
Extrinsic ligaments include;
Iliofemoral Ligament—Reinforces anterior side of the hip joint
Ischiofemoral Ligament—Supports posterior side of the hip joint
Pubofemoral Ligament—Triangular thickening of the inferior portion of the articular capsule
Ligament of the Head of the Femur—Links the center of the head of the femur with the acetabulum
Hip replacement is a surgical procedure that replaces a damaged joint with an artificial prosthetic device
Severe arthritis, trauma, fractures, and bone tumors are common reasons for the procedure
Total hip replacement removes and replaces the head of the femur and reconstructs the acetabulum
Partial hip replacement removes only the head of the femur, while leaving the acetabulum intact
After surgery, patients generally begin physical therapy right away and may return to normal activities within 2–8 weeks